Mammalian Growth Hormone-Releasing Hormone Indirectly Stimulates Sex Steroid Production in Tilapia

Abstract.— Fish possess a growth hormone similar to mammalian growth hormone, and the presence of a growth hormone-releasing hormone-like material in the brain has been demonstrated in several teleost species. We investigated the effect of a mammalian growth hormone-releasing hormone on serum estradiol-17β and testosterone concentrations in tilapia Oreochromis mossambicus and a hybrid O. niloticus × O aureus because growth hormone has been implicated in the regulation of gonadal functions in teleosts. Three hours after injecting the releasing hormone, male and female serum testosterone concentrations significantly increased compared to controls, while serum estradiol-17β concentrations increased significantly only in females. These increases were commensurate with respective serum steroid concentrations in fish injected with gonadotropin releasing-hormone. Studies utilizing hypophysectomized fish resulted in non-detectable levels of serum sex steroids in fish treated with the growth hormone-releasing hormone; however, significant increases occurred in fish treated with human chorionic gonadotropin. Similarly, gonadal tissue incubated with growth hormone releasing hormone had non-detectable levels of sex steroids in the media, whereas gonads incubated with human chorionic gonadotropin had significant increases in sex steroid concentrations. These studies suggest that growth hormone-releasing hormone acts at the level of the pituitary. Although mammalian growth hormones have been shown to increase serum gonadotropic hormone concentrations, this study provides evidence that a mammalian growth hormone-releasing hormone has the ability to indirectly increase sex steroid levels in fish.     

Effects of Dietary Protein Levels on Gonad Maturation, Size and Age at First Maturity, Fecundity and Growth of Nile Tilapia

Six-week-old Nile tilapia (Oreochromis niloticus) fry with an average weight (SD) of 0.51(0.2) g were reared for 140 days on five formulated, isocaloric diets of different protein levels (25, 30, 40 and 45% by dry weight). Fish fed diets of higher protein levels (40 and 45%) showed better growth and feed conversion ratio than those on lower protein levels. Fast-growing fish matured earlier. Maturation rate was affected by the dietary protein levels. Males matured earlier than females: the first mature males were recorded when they were 14 weeks old, whereas the females matured after 18 weeks. In both sexes, mean percentage of mature fish rose with increasing dietary protein level, the percentage of mature males being higher than that of the females. Similarly, the percentage of mature fish rose with the increasing age of fish, with more than 50% males and females mature at the age of 22 and 24 weeks, respectively, the exception being the 25% protein diet fed fish, where the percentage of mature fish was below 50%. In all treatments, spawning was initiated when the fish were 22 weeks old. Smallest size at spawning of males and females was 9.2 cm (13.1 g) and 8.1 cm (8.9 g), respectively, and dietary protein levels influenced the size of fish at first maturity. For both sexes, no difference was found in the gonado-somatic index (GSI) among different treatments. Fecundity increased with increasing dietary protein levels, but significant differences were found only between 40–45% and 25–35% dietary protein levels. The relative fecundity (eggs g^–1 female) was higher at the lower dietary protein levels (25–35%) than at the higher dietary protein levels (40–45%). The dietary protein levels did not have any significant influence on the size and weight of mature eggs. The chemical composition of fish and mature ovaries was significantly influenced by the dietary protein level.     

Effect of Luteinising Hormone-Releasing Hormone Analogue and Human Chorionic Gonadotropin on Ovulation, Plasma and Ovarian Levels of Gonadal Steroids in Greenback Flounder Rhombosolea tapirina

Female greenback flounder Rhombosolea tapirina were treated with either des Gly¹⁰ [D-Ala⁶] LHRH ethylamide (LHRH-a) at 50 or 100 pg/kg intraperitoneal injection (ipi), LHRH-a cholesterol pellet (LHRH-a pellet) 100 μg/kg implanted intraperitoneally, or human chorionic gonadotropin (hCG) 1,000 IU/kg ipi. Treatment with hCG, LHRH-a (50 μg/kg) ipi and LHRH-a pellet increased the total number of ovulations above control levels. LHRH-a (100 μg/kg) ipi was not consistently more effective than the control and both LHRH-a (50 μg/kg) ipi and LHRH-a pellet induced more ovulations than LHRH-a (100 μg/kg) ipi. Of those fish that ovulated, most ovulated more than twice, and most ovulations occurred at daily intervals. Oocyte diameters increased and oocyte stage advanced significantly in response to all exogenous hormone treatments. This was accompanied by increases in plasma and ovarian levels of 17β-estradiol (E₂, and in most cases, plasma and ovarian levels of testosterone (T). Plasma and ovarian levels of 17,20β-dihydroxy-4-pregnen-3-one (17,20βP) were not consistently elevated in association with reproductive events.     

Electrical Conductivity of Frozen Shrimp and Flounder at Different Temperatures and Voltage Levels

Electrical conductivity (EC) is an important property during ohmic thawing of seafood. EC of frozen flounder, tiger and white shrimp, and shrimp shells at different voltages and temperatures (T) was measured. The materials were homogenized in a blender. PVC tubes (lengths: 4.1 to 5.6 cm, diameter: 1.5 cm) were filled with the material and fitted with circular stainless steel electrodes connected to a DC power supply. The tubes were frozen to constant Ts (-16 to -4°C). Voltage gradient (VL, 8.3 to 122 Volts/cm) and current were measured with multimeters. The calculated specific conductivity (SpC = Siemens/m) depended strongly on temperature. VL had a small effect on SpC. An equation of the form SpC = a + b VL + c exp(d/T + f/T²) was fitted to the data. R² values for shrimp shells, tiger shrimp, and flounder were 0.96, 0.83, and 0.64, respectively.     

壳寡糖对南美白对虾生长和血清生化指标的影响

为研究壳寡糖对南美白对虾(初始体重约1.23 g)的生长和血清生化指标影响,设置了含壳寡糖0 mg/kg、125 mg/kg、250 mg/kg、500 mg/kg、1000 mg/kg的5组试验饲料,经过8周的饲养实验。结果表明,不同含量的壳寡糖对南美白对虾的增重率、特定生长率、饲料系数和成活率均无显著影响(P>0.05);对南美白对虾血清中的肌酐、葡萄糖、钙离子、总胆固醇、甘油三脂和低密度脂蛋白胆固醇均无显著影响,但可使高密度脂蛋白胆固醇显著增加,促进脂类代谢;综合试验结果得出饲料中壳寡糖添加250~500 mg/kg为宜。     

养殖鱼类血清生长激素水平与锌含量的关系研究

本文应用放射免疫分析法测定6种养殖鱼类血清中生长激素水平，采用原子吸收光谱法测定了相应血清中的锌含量。实验结果显示，养殖鱼类血清中的生长激素水平与锌含量呈正相关。     

Replacement of Fishmeal with Soybean Meal in Male Tilapia (Oreochromis niloticusxO. aureus) Fingerling Diets at a Suboptimal Protein Level

A feeding trial was conducted to study the feasibility of using soybean meal (SBM) to replace fish meal (FM) as a protein source for tilapia feeds containing 24% dietary protein. Replacement levels were 0%, 33%, 67% and 100%. At each replacement level, methionine was either supplemented up to the amount that the 100% FM protein diet contained or not supplemented. The experiment was carried out for eight weeks in a recirculated water system. Fish fed diets in which 100% of the FM was replaced with SBM either with or without methionine supplementation had significantly ( P < 0.05) lower weight gain, feed conversion ratio, protein efficiency ratio and protein digestibility than that of the groups fed the diets containing FM as the sole source of protein. Also, fish fed diets in which 67% and 33% of the FM was replaced with SBM did not differ significantly ( P > 0.05) from that of the control group. These data suggest that when dietary protein level was suboptimal (24%), up to 67% of the FM protein in tilapin feeds can be replaced by hexane-extracted SBM protein without any adverse effect on tilapia growth and feed conversion ratio.     

奥尼罗非鱼血清免疫球蛋白的纯化及分子量的初步分析

通过饱和硫酸铵盐析结合 Sephadex G-200柱层析的方法,纯化制备了健康非免疫状态下奥尼罗非鱼的免疫球蛋白,进行变性还原条件下的聚丙烯酰胺凝胶电泳(SDS-PAGE)和免疫印迹试验对血清的免疫球蛋白进行初步分析,发现SDS-PAGE电泳条件下血清重链分子量为85 kD,轻链分子量为30 kD.如果罗非鱼血清免疫球蛋白在自然状态与其他硬骨鱼类一样也为四聚体,那么其总分子量的理论值应为920 kD.     

Growth and Survival of Juvenile Orconectes virilis and Orconectes immunis at Different Temperatures1

Culture of orconectid crayfishes in the midwestern USA offers the potential of contributing to a year-round supply of fresh product as summer/fall production would augment winterhpring production in the southern USA. However, relatively little basic biological information exists for this potential new aquaculture crop. In this study, the authors reared juvenile (third instar) Orconectes virilis and Orconectes immunis at either 10, 15, 20, 25 or 30 C and measured weight gain and survival over a 21 day period. Orconcctes immunis juveniles were larger than O. virilis at the third instar and gained weight more rapidly in this experimental system. Gains in weight and length for both species increased as temperature increased from 10 to 25 C. Both values were lower in crayfish reared at 30 C, though number of molts was the same in crayfish reared at 25 or 30 C. Thus, there appears to be a bioenergetic cost of rearing orconectid crayfishes in temperatures above 25 C. Further, incremental growth with successive molts was influenced by water temperature.     

Growth and Chemical Composition of Spirulina Maxima and Spirulina Platensis Biomass at Different Temperatures

The influence of temperature on growth and biomass composition of two species of Spirulina, S. maxima and S. platensis used for food was studied. A 4L fermenter with temperature and agitation control was used to cultivate both species. Under continuous light, maximum cell production of 2.4 g l^–1 was verified for both cultures studied at temperatures above 25 °C: S. maxima (30 °C and 35 °C) and S. platensis (25 °C and 30 °C). An accentuated lag phase was observed for all cultures at lower temperatures (15–20 °C), and a maximum biomass production of 1.5 g l^–1 was achieved. It was also observed that an increase of temperature caused a marked decrease in protein content, while carbohydrate synthesis was stimulated. The concentration of -linolenic acid varied from 11–16% for S. maxima and from 12–14% for S. platensis, at the optimum growth temperatures. Greater culture volumes were also studied in order to compare the performance of glass and plastic containers. At optimum growth temperature, S. maxima produced the same cell growth and similar final biomass composition.     

Examination of the Effects of Dietary Protein and Lipid Levels on Growth and Stress Tolerance of Juvenile Tilapia,Oreochromis niloticus

Tilapia is the second most consumed farmed fish after carp and the most widely grown farmed fish. However, significant price increases in ingredients in recent years threaten profitability of the industry because dietary costs are approximately 60% of production costs. Therefore, the objective of this study was to optimize dietary protein and lipid levels of juvenile tilapia cultured in high‐intensity recirculating‐water system and assess dietary effects on stress tolerance. To achieve this objective, a factorial treatment design with diets formulated to contain three levels of dietary protein (28, 32, and 36%) and three levels of dietary lipid (3, 6, and 9%) was employed. Juvenile tilapia (34.5 ± 0.4 g initial weight) were randomly assigned to each of 24 tanks and fed one of the nine diets, three feedings per day to apparent satiation, 6 d/wk for 12 wk. Fish were weighed and counted every 3 wk and feed consumed recorded weekly. Tilapia weight gain, feed conversion, feed intake, and proximate composition were significantly affected by diet. Following the feeding trial, tilapia were subjected to a 24 h simulated live haul where fish were stocked into a static water system at 0.24 kg/L of water. Glucose, lactate, and cortisol measurements were taken at time 0, 24, and 72 h after fish were placed into hauling containers. There was significant effects (P < 0.05) of crude lipid and crude protein on blood chemistry parameters. These data indicate that practical diet formulations can be improved to enhance growth rates, production of tilapia, and stress response during live hauls.     

Overview of Fish Growth Hormone Family. New Insights in Genomic Organization and Heterogeneity of Growth Hormone Receptors

Growth hormone (GH), prolactin (PRL) and somatolactin (SL) are single chain proteins structurally and functionally related. Fish PRL and GH receptors (PRLR, GHR) have been characterized in several fish species. There is limited evidence of fish PRLR isoforms, but emerging data support the existence of different GHR variants. In gilthead sea bream, black sea bream, turbot and fugu, but not in zebrafish, GHR has retained an exclusive fish intron (10/10A). In gilthead sea bream and turbot, this intron is not alternatively spliced, but the black sea bream intron is either removed or retained during mRNA processing, resulting in a long GHR isoform with a 31 amino acid insertion that does not alter the open reading frame. This or any other GHR variant are not found in gilthead sea bream, but a truncated anchored form has been reported in turbot. The latter GHR isoform comprises extracellular and trans-membrane domains, the first 28 amino acids of the intracellular domain and 21 divergent amino acids before a stop codon. This GHR variant is the result of alternative splicing, being the 3′ UTR and the divergent sequence identical to the sequence of the 5′ end of the 9/10 intron. The physiological significance of different fish GHR isoforms remains unclear, but emerging data provide suitable evidence for season and nutrition related changes in the somatototropic axis activity. The up-regulation of circulating GH together with the decrease of plasma titres of insulin-like growth factor-I (IGF-I), an altered pattern of serum IGF binding proteins and a reduced expression of hepatic IGF-I and GHRs represent a mechanism conserved through vertebrate evolution. It secures the preferential utilization of mobilized substrates to maintain energy homeostasis rather than tissue growth. Somatolactin also changes as a function of season, ration size, dietary amino acid profile and dietary protein source creating opposite plasma GH and SL profiles. There is now direct evidence for a lipolytic effect of fish SL, acting at the same time as an inhibitory factor of voluntary food intake. Indeed, long-term feeding restriction results in the enlargement of the summer GH peak, whereas the SL rise coincident with shortened day length is delayed in juvenile fish until late autumn. These findings agree with the idea that SL may act as a marker of energy surplus, priming some particular process such as puberty onset. However, it remains unclear whether SL works through specific receptors and/or dimers or heterodimers of GH and PRL receptors.     

A Probiotic Cocktail as a Growth Promoter in Nile Tilapia (Oreochromis niloticus)

The aim of this study was to evaluate Lactobacillus acidophilus, Streptococcus thermophilus, Bifidobacterium bifidum, and yeast Saccharomyces cerevisiae singly and in combination as probiotic supplements in Nile tilapia (Oreochromis niloticus) fingerling diets. All the probiotic-supplemented diets resulted in growth higher than the control. Best growth rate, food consumption, and food conversion (P < 0.05) were in the group fed a cocktail of the three bacteria. Feed cost, return on weight gain, and profit margin increased in fish groups fed diets inoculated with probiotics. Supplementation with Lactobacillus acidophilus, Bifidobacterium bifiduim, and the three-bacteria cocktail were most effective in eliminating mortality in an A. hydrophila challenge.     

Effects of Feeding Frequency on Apparent Energy and Nutrient Digestibility/Availability of Channel Catfish,Ictalurus punctatus,Reared at Optimal and Suboptimal Temperatures

This study examined the effects of feeding frequency (daily versus every other day [EOD]) on nutrient digestibility/availability of channel catfish, Ictalurus punctatus, reared at optimal (30 C) and suboptimal (24 C) temperatures. A 28% protein practical diet was used as the test diet, and chromic oxide was used at 0.75% of the diet as a maker. Twenty channel catfish of a mean weight of 141 g/fish were stocked into 12 flow‐through aquaria (110 L). Fish were fed daily or EOD to apparent satiation for 7 d before fecal samples were collected by the dissection method. Fish fed EOD to apparent satiation consumed more diet on days fed than those fed daily, and fish reared at 30 C consumed more diet than those reared at 24 C. Neither feeding frequency nor water temperature significantly affected apparent digestibility coefficients for energy and protein and apparent availability coefficients for total amino acids. Results show no advantage by feeding EOD over feeding daily on nutrient digestibility and diet utilization efficiency.     

以色列红罗非鱼与其他罗非鱼群体杂交子一代在海水中生长性能分析

利用以色列红罗非鱼品系(Israel strain of red tilapia,R)、吉富品系(GIFT strain of Nile tilapia,J)(Oreochromis niloticus)、奥利亚罗非鱼(Blue tilapia,A)(O.aureus)、尼罗罗非鱼(Nile tilapia,N)(O.niloticus)等群体,构建了具有广泛遗传变异罗非鱼育种基础群体。采用人工定向交尾技术,获得了15个以色列红罗非鱼群体内和65个以色列红罗非鱼群体及其他群体间杂交全同胞家系。待家系平均体重5-8 g时进行标记,每个家系随机取样40尾标记个体放入养殖池中,采用逐渐提高盐度驯化至养殖盐度为28,养殖150 d后进行生长性能测试以及杂交和体重生长遗传参数分析。结果显示,在研究的所有群体内和群体间的交配组合中,以色列红罗非鱼品系(♀)与尼罗罗非鱼(♂)杂交的杂交组合(R×N)子一代生长速度最快,优于其他杂交组合,其平均体长、平均体重和绝对增重率分别为24.44 cm、385.23 g和4.94 g/d;ANOVA和LSD多重比较分析结果显示,杂交组合间在体长、体重指标上均达到差异极显著(P<0.01),R×N与除J×R杂交组合外的其他3个杂交和1个群体自繁组子一代两两间存在显著差异(P<0.05)。利用实验构建的80个家系共2496个个体体重数据,考虑家系标记时的平均体重、池塘、雌、雄等因子,建立了遗传参数分析模型,估计体重的遗传力为0.46±0.07,属于中等遗传力。因此,利用本研究收集的罗非鱼基础群体,开展罗非鱼在海水中生长性状选育,具有很大的遗传改良潜力。     

Clonidine Mects Growth Hormone and Growth in Juvenile Coho Salmon Oncorhynchus kisutch

Growth hormone concentrations in juvenile cocho salmon were determined after intraperitoneal injections (yearlings; age 1+) and oral treatments (yearlings and fry; age 0+) with clonidine. Weights and lengths were also measured in coho juveniles fed diets supplemented with clonidine.
Plasma growth hormone concentration increased significantly (78.2%) 24 h after injection. Yearlings fed clonidine showed a significant increase (136%) in plasma growth hormone after 14 days, and levels remained elevated through 28 days (116%) before dropping to control levels at 42 days. Coho yearlings fed clonidine showed no significant increase in growth compared to controls after 56 days of treatment, but coho fry were significantly heavier (33%) and longer (8%) after 70 days.     

Growth Performance,Biochemical Responses,and Skeletal Muscle Development of Juvenile Nile Tilapia,Oreochromis niloticus,Fed with Increasing Levels of Arginine

Tilapia, Oreochromis niloticus, is among the fish species with high potential for aquaculture in intensive farming, and Brazil is among the largest producers worldwide. Some of the amino acid requirements in practical diets for tilapia are still unknown. Thus, this study determined the dietary arginine requirements for Nile tilapia juveniles based on growth performance, hematological and biochemical responses, and muscle growth. Three hundred Nile tilapia juveniles (2.95 ± 0.79 g) were distributed into 20–500 L fiberglass aquaria and fed five extruded isoproteic (28% crude protein) and isoenergetic (3160 kcal/kg) diets formulated to contain 0.95, 1.10, 1.25, 1.40, and 1.55% arginine. Based on the quadratic regression analysis, the best results in weight gain, feed conversion, protein efficiency ratio, and protein retention were estimated in fish fed diets containing 1.36, 1.34, 1.36, and 1.37% arginine, respectively. The best amino acid body retention values were estimated in fish fed diets containing 1.31–1.37% arginine. Muscle growth occurred mainly by hyperplasia in fish fed 0.95% arginine, whereas reduction in the hyperplasia time and signs of hypertrophy occurred in fish fed 1.10–1.55% arginine diets. It was concluded that a diet with 1.36% of arginine (with 1.53% lysine in diet) meets the requirements of Nile tilapia juveniles.     

Growth Response of Tilapia Fed Diets Rich in High-Lysine Corn and Corn Gluten

Abstract

The purpose of this study was to find out if fish meal is necessary in tilapia diet for good growth response. Five experimental diets (32% protein) containing 46-51% high-lysine corn, 20% corn gluten meal, supplemented with soy grits and synthetic amino acids, with and without fish meal were formulated. The diets were fed to tilapia with average initial weight of 13 g for 70 days in aquaria. Weight gain expressed as percentage increase after 70 days or as grams/day, feed conversion ratio, and protein efficiency ratio were equal (P > 0.05) to a commercial feed (36% protein) for all experimental diets. It appears that 32% protein diets with 46-51% high-lysine corn and 20% corn gluten meal were adequate for tilapia based on weight gain, feed conversion ratio, and protein efficiency ratio, and that fish meal is not necessary for tilapia feed to obtain good growth response.     

维生素E和硒对吉富罗非鱼(Oreochromis niloticus)幼鱼生长及血清抗氧化酶活性的影响

本研究采用2×5双因子试验设计,即在基础饲料中分别添加0和0.15 mg/kg的Se,每一Se水平下分别添加0、30、60、90、120 mg/kg的维生素E(VE),共制成10种试验饲料,饲喂平均初始体质量为(0.37±0.01)g的吉富罗非鱼(Oreochromis niloticus)70 d,每组设3个重复,每个重复组50尾吉富罗非鱼,其中饲喂未添加Se和VE的基础饲料组为对照组。结果表明,(1)VE对吉富罗非鱼幼鱼增重率、特定生长率、摄食量和饲料系数均有显著影响(P0.05),就生长性能而言,单独添加VE的适宜范围是63.86–70.58 mg/kg。Se对吉富罗非鱼的增重率、特定生长率的影响不显著(P0.05),但在VE添加量为0 mg/kg的试验组中,硒的添加使吉富罗非鱼增重率高于对照组。VE和Se对吉富罗非鱼生长的交互作用没有显著影响(P0.05)。(2)VE对谷胱甘肽过氧化物酶(GSH-PX)和过氧化氢酶(CAT)活性有显著影响(P0.05),总超氧化物歧化酶(T-SOD)和CAT活性随VE添加量的增加呈上升趋势。而Se可显著影响T-SOD和GSH-PX的活性(P0.05),在VE添加量范围60–90 mg/kg时,加Se试验组的T-SOD、GSH-PX和CAT活性较不加Se组有所上升。VE和Se对GSH-PX活性的影响具有显著的交互作用(P0.05)。在本研究条件下,VE和Se对吉富罗非鱼的生长及抗氧化有一定促进作用,二者联合使用,没有协同促生长作用,但抗氧化作用得到进一步加强。     

美国罗非鱼市场概况及我国出口罗非鱼展望

近年来，罗非鱼在美国市场的需求量逐步增加，其中尤以新鲜冷冻的罗非鱼片需求最为强劲。罗非鱼在进入美国市场初期，仅限于以活鱼方式在东方人经营的商店或餐厅销售，其后，由于罗非鱼价格合理，供应稳定，口味符合消费者需求，发展至今，罗非鱼及其加工制品已进入“美国各州的西餐厅、海产店的活鱼水箱中，诸如斑点叉尾Hui、鲑鳟鱼等各种养殖鱼类相竞争。业内人士估计，罗非鱼这种价廉味美的优质养殖鱼类不久将来即可占领美国市场大多数的海洋餐厅和海鲜店。